1. Field of the Invention
The present invention relates to an inspection apparatus for inspecting an inspected object based on a waveform quality of a signal that the inspected object outputs. The present invention especially relates to an inspection apparatus capable of obtaining stable results by automating the inspecting steps including the sensory inspection.
2. Description of the Related Art
On the delivery inspection line of the communication device (e.g., multiplexer IC, demultiplexer IC, modulator driver IC, very high-speed logic IC, or the like) used in the transmission/reception of the digital communication (See Document 1 mentioned below, for example.), and on the delivery inspection line of the communication measuring apparatus including the communication device (e.g., pulse pattern generating apparatus, bit error rate measuring apparatus, or the like) (See Document 2 mentioned below, for example.), and so forth, the inspection is carried out by detecting the waveform quality (also called as the “waveform quality” hereinafter) based on the waveform image that is called an eye pattern (See JP-A-2000-295298, for example.). In particular, in the high-speed communication device (a bit rate of which exceeds 10 [Gbps], for example), the eye pattern is often used as the index of the waveform quality.
FIG. 8 is a view showing a configuration of an inspection apparatus in the related art. A high-speed communication device 1 is an inspected object, and outputs the pulse pattern signal that has a high level and a low level. A power supply section 2 supplies an electric power to the communication device 1, and outputs a control signal (current, voltage, or the like).
An oscilloscope 3 generate the eye pattern by measuring the signal fed from the communication device 1, and derives the characteristic value indicating the waveform quality based on the eye pattern. Also, the oscilloscope 3 displays the eye pattern and a characteristic value on a display screen. A personal computer 4 records the inspection results of the communication device 1.
An operation of such inspection apparatus will be explained hereunder.
First, the inspector manually operates the power supply unit 2 and causes the unit to output a predetermined power and a plurality of control signals to the communication device 1. Here, the control signal can be regarded as a parameter applied to determine the waveform quality of the communication device 1. For example, there are a voltage used to control an amplitude, a voltage used to control a cross point, a voltage used to control an offset, a voltage used to control respective levels at which an upper limit value and a lower limit value of the waveform are clipped, and the like.
Then, the oscilloscope 3 measures the signal being output from the communication device 1, and displays the eye pattern and the characteristic value. The characteristic value indicates the waveform quality and is derived from the eye pattern. Also, a section for detecting the typical characteristic values is incorporated into the normal oscilloscope 3 that is commercially available. As the typical characteristic values, there are an amplitude (difference between the high level and the low level), an offset (difference between a 0 [V] level and an intermediate level between the low level and the high level), a cross point, an S/N (signal to noise ratio), a jitter, a rise time, a fall time, etc., for example. Also, in most cases these characteristic values are provided in the specification of the communication device.
Then, the inspector checks the eye pattern and the characteristic value displayed on the oscilloscope 3 with the eye. Also, the inspector inputs the parameters such as the voltage value, the current value, etc. of the control signal, the characteristic values, the acceptance/rejection result, and others into the personal computer.
Also, when the characteristic values do not satisfy the values specified in the specification, the inspector manually operates the power supply unit 2 while observing the eye pattern and the characteristic values to vary the parameter of the communication device 1.
In this case, in the communication device 1, for example, when only the voltage as the parameter to adjust the offset is varied to increase the offset, the cross point and the amplitude are also changed. In addition, the offset is closely related with other characteristics such as the S/N, the jitter, etc. Therefore, a plurality of parameters must also be operated only when one characteristic value should be improved. Of course, the parameters are handled while checking respective values of a voltmeter, a current meter (both not shown), etc. provided on the power supply unit 2 with the eye to prevent the event that the excessive voltage or current is output to the communication device 1.
Meanwhile, it is not always enough that merely the characteristic values can be kept within requirements in the specification. Ideally, the amplitude and the cross point are better the closer these values are set to the set values (e.g., the amplitude 5 [v], the cross point 50[%]) within the range described in the specification, the S/N is better the larger the value becomes, and the jitter is better the smaller the value becomes, for example.
Also, the inspection must be conducted by adjusting the parameters with regard to the characteristic values that are not described in the specification and are not detected by an analyzing section (not shown)(referred to as “feature amount” hereinafter), and repeating the adjustment to get the high waveform quality. In other words, if the feature amount is not good even though the characteristic values satisfy the specification, in some cases the inspected object is regarded as the defective unit. Therefore, the inspector manually operates a plurality of control parameters while the feature amount and the characteristic value with the eye to execute the adjustment/inspection that are required to get the high waveform quality.
The following documents are referred to as a related art.
[Document 1] Aoki and four others, “DEVELOPMENT OF HBT-IC MODULES FOR 50-GBPS OPTICAL COMMUNICATION SYSTEMS”, Yokogawa Technical Report English Edition, Yokogawa Electric Corporation, 2002, No. 34, pp. 1–6
[Document 2] Tsutsumi and five others, “Development of Ultra-compact 10 Gbit/s Bit Error Rate Testers”, ANDO TECHNICAL BULLETIN, Ando Electric Co., Ltd., 2004 January, No. 73, pp. 18–22
JP-A-2000-295298 (Paragraph [0002]–[0007], FIG. 3)
In the inspection steps, the waveform image and the characteristic values are displayed automatically on the oscilloscope 3, and the voltage value, the current value, etc. used to control the communication device 1 are displayed automatically on the power supply unit 2. However, in order to not only satisfy the specification but also get the higher waveform quality, the inspector must manually operate a plurality of parameters of the power supply unit 2 while observing them with the eye to search the optimum combination of parameters. Therefore, following problems resided in the related art.
The communication device 1 is a multi-input/multi-output system because there is the multi-to-multi relationship between the control parameters that the inspector can operate and the characteristic values and the feature quantities that are derived from the waveform image. Therefore, it is difficult for the inspector to handle the parameters. Also, in order to control the characteristic values and the feature quantities that are derived from the waveform image, the inspector must operate depending on the know-how and the intuition that the inspector acquires based on the experience. As a result, such a problem existed that the waveform quality is varied. In addition, there existed the problem that the inspection time is varied and prolonged according to a difference in the experience level of the inspector.
Besides, since the inspection that depends on the visual inspection, the personal experience, etc. (sensory inspection) is applied, there also existed following problems that are involved in the sensory inspection itself.
(1) Variation caused by the individual differences. There is a variation caused by the individual difference in the feeling and the discriminating power. Also, there is a lack of balance such that which ones of the characteristic values and the feature quantities should be adjusted mainly.
(2) Influence of the feeling. The five senses are affected by the mood of that day, the inspector's living environment, the state of inspector's health, the fatigue, and others. Therefore, the criteria applied to the inspection are changed every time.
(3) Variation in the expression. Even when the inspector decides that the waveform quality is “very excellent”, the individual difference lies in the boundary that is applied to decide whether or not the term “very” should be used. Also, one inspector will give an exaggerated expression whereas the other inspector will give an opposite expression. Because it is difficult to give a concrete expression in the sensory inspection, the individual difference in expression largely appears in the sensory inspection.
(4) Change attendant to a degree of mastery. In the situation that the inspector is versed in the operation, normally such inspector executes the adjustment/inspection without thinking to get the higher waveform quality. Also, a metal state of the inspector is influenced by the change in the external environment. For example, the criteria applied to the inspection become extremely strict when a complaint, or the like is made from the user, and others.